Fatal gas line mix-up: How to avoid
making this "gastly" mistake

From the December 16, 2004 issue

Problem: Recently, we learned that an oxygen flow meter
had been forced into a nitrous oxide wall outlet that was directly
adjacent to an oxygen outlet in a radiology suite. The oxygen
flow meter's index safety system, designed to assure connection
only to oxygen wall outlets, was broken at the time of insertion.
(All gas cylinders, flow meters, and wall outlets utilize a
PIN index safety system, DIAMETER index safety system, or other
system meant to avoid cross utilization of sources and components) Additionally, the technician was unable to distinguish
blue (nitrous oxide) from green (oxygen) because the radiology
suite was dimly lit in preparation for a CAT scan. Sadly, instead
of receiving oxygen, the patient died of nitrous oxide poisoning.
Although the index safety systems and color-coding of gas cylinders
have been in use for years as constraints or cues to prevent
this type of error, there have been numerous similar events
of hypoxic injury reported anecdotally and appearing in the
literature. Broken or modified pins used with gas cylinders
also have allowed misconnections.

At first glance, you may ask, "Why is nitrous oxide
available in radiology?" Indeed, it may be possible to
eliminate nitrous oxide in some locations outside of the operating
room (OR). However, mix-ups between other gases accessible
through wall outlets, including air (and even vacuum outlets),
would still be possible. Also, many anesthesiologists now
administer anesthetics in locations outside the OR, so it
may not be possible to remove this useful anesthetic from
all non-OR settings. Invasive procedures are being performed
more frequently in radiology, sometimes replacing the need
for surgical procedures, and anesthesia coverage for endoscopic
procedures has become more common. General anesthetics are
also delivered in bronchoscopy suites, cardiac catheterization
laboratories, plastic surgery clinics, and other locations
where invasive procedures are performed. As one of our consulting
anesthesiologists pointed out, "A basic principle in
anesthesia is that no single agent is optimal, so we use multiple
agents and, through their synergy, obtain a more favorable
benefit-side effect profile. Removal of nitrous oxide in locations
outside of the OR could contribute to two different standards
of anesthesia care."

Separating nitrous oxide and oxygen wall outlets is one option,
but it may not be economically feasible to relocate all of
the gas lines within the walls in existing facilities. Eliminating
access to nitrous oxide from the wall outlets in locations
outside the OR is another option, but this could result in
new risks and concerns. First, anesthesiologists would have
to use cylinders of nitrous oxide if needed. With wall outlets,
the multiple gas connections are spaced close to each other
so that the tubing running from the gas source to the anesthesia
equipment is localized and compact. If gas sources were separate,
the tubing would not be localized, thus creating new hazards
such as difficult access around equipment, tripping over tubing,
accidental disconnection, obstruction from kinking, and tethering
of equipment. The replacement of nitrous oxide cylinders and
the risk of an empty tank also could create a new set of concerns.

Administration of the wrong gas has also been attributed
to connecting the patient's tubing to the wrong flow meter,
especially if color-coded "Christmas Tree" adaptors
are used. Green adaptors are meant for oxygen, yellow adaptors
for air. Although flow meters may be designed to connect to
just one type of gas, the threading for connection between
the flow meter and the adaptor is universal, so the wrong
color adapter could be used. Thus, if staff rely on the color
of the adapter to guide connections, the oxygen tubing could
be misconnected to an air flow meter if a green adapter has
been used in error.

Safe Practice Recommendation: Since it's likely that
nitrous oxide will continue to be available in various locations
throughout the hospital, action must be taken to prevent a
deadly mix-up. First, be sure to standardize the type of flow
meters, regulators, and connectors used throughout the facility,
and use only those with intact index safety systems to help
prevent misconnection. Assure that gas connections are observable
(not hidden under a table or behind a drape) and that the
labeling of all gas connections and sources is prominent and
visible under the conditions that are actually present during
use (e.g., dim lighting, crowded spaces). If a patient does
not respond as expected to treatment with supplemental oxygen,
consider the possibility that the wrong gas (or no gas) is
being administered and check the flow meter and tubing connections.
Also, consider using clear Christmas Tree adapters, forcing
the user to look at the flow meter and wall connection itself.
Also, a bad outcome from a nitrous oxide/oxygen switch would
be less likely if an oxygen saturation monitor was used to
provide an early alarm of hypoxia.

Biomedical engineering experts should perform regular preventive
maintenance on gas wall outlets, gas cylinders, flow meters,
and other related equipment to assure that all connections
and connectors are intact and in good working condition. Only
trained and certified personnel should be allowed to service,
maintain, and use this equipment. Perhaps it's also time to
consider new standards. While the index safety system has
worked reasonably well, in light of adverse events like the
one cited above, new standards may be needed to make it impossible
for gas line misconnections. Changing the materials used to
manufacturer pins and attachments so they are less likely
to break or wear out is just one example of an improvement
that could be made with renewed scrutiny. The Association
for the Advancement of Medical Instrumentation (AAMI) has
just approved a committee to develop national standards for
tubing connectors, which will also address this important
safety issue.